Seasonal variation in biomass and carbohydrate partitioning of understory sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis) seedlings

We investigated seasonal patterns of biomass and carbohydrate partitioning in relation to shoot growth phenology in two age classes of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britt.) seedlings growing in the understory of a partially harvested forest. The high root:shoot biomass ratio and carbohydrate concentration of sugar maple are characteristic of species with truncated growth patterns (i.e., cessation of aboveground shoot growth early in the growing season), a conservative growth strategy and high shade tolerance. The low root:shoot biomass ratio and carbohydrate concentration of yellow birch are characteristic of species with continuous growth patterns, an opportunistic growth strategy and low shade tolerance. In both species, starch represented up to 95% of total nonstructural carbohydrates and was mainly found in the roots. Contrary to our hypothesis, interspecific differences in shoot growth phenology (i.e., continuous versus truncated) did not result in differences in seasonal patterns of carbohydrate partitioning. Our results help explain the niche differentiation between sugar maple and yellow birch in temperate, deciduous understory forests

In vivo and in situ rhizosphere respiration in Acer saccharum and Betula alleghaniensis seedlings grown in contrasting light regimes

A perfusive method combined with an open-system carbon dioxide measurement system was used to assess rhizosphere respiration of Acer saccharum Marsh. (sugar maple) and Betula alleghaniensis Britton (yellow birch) seedlings grown in 8-1 pots filled with coarse sand. We compared in vivo and in situ rhizosphere respiration between species, among light regimes (40, 17 and 6% of full daylight) and at different times during the day. To compute specific rhizosphere respiration, temperature corrections were made with either species-specific coefficients (Q10) based on the observed change in respiration rate between 15 and 21°C or an arbitrarily assigned Q10 of 2. Estimated, species-specific Q10 values were 3.0 and 3.4 for A. saccharum and B. alleghaniensis, respectively, and did not vary with light regime. Using either method of temperature correction, specific rhizosphere respiration did not differ either between A. saccharum and B. alleghaniensis, or among light regimes except in A. saccharum at 6% of full daylight. At this irradiance, seedlings were smaller than in the other light treatments, with a larger fine root fraction of total root dry mass, resulting in higher respiration rates. Specific rhizosphere respiration was significantly higher during the afternoon than at other times of day when temperature-corrected on the basis of an arbitrary Q10 of 2, suggesting the possibility of diurnal variation in a temperature-independent component of rhizosphere respiration

Physiological responses of Vismia guianensis to contraisting light environments.

Investigou-se por um período de 60 dias em câmara de crescimento, sob alto (800-1000 μmol m-2 s-1) e baixo (120-200 μmol m-2 s-1) regimes de luz os padrões de crescimento e distribuição de biomassa e as trocas gasosas de Vismia guianensis (Aubl.) Choisy, uma árvore de porte médio, comum como planta invasora de pastagens, áreas agrícolas abandonadas, e clareiras de floresta na Amazônia brasileira. Não foram detectadas diferenças em assimilação de CO2 na curva de resposta a luz entre plantas cultivadas sob alta e baixa radiação. No entanto, a respiração foi maior em plantas sob alta radiação. A taxa de crescimento relativo foi inicialmente similar entre regimes de luz, tomando-se maior para alta radiação nas avaliações subsequentes. A área foliar por unidade de massa total da planta e por unidade de massa da folha foram maiores para baixa radiação. A proporção de biomassa alocada para folhas foi semelhante entre tratamentos, enquanto a alocação de biomassa para as raízes foi maior em alta radiação e a alocação de biomassa para hastes e pecíolos foi maior em baixa radiação. Estes resultados sugerem que as respostas dessa espécie a variações nas condições de luminosidade são importantes para o seu sucesso em ambientes naturais e agrícolas ou a sua resposta a práticas de controle

Leaf- and plant-level carbon gain in yellow birch, sugar maple, and beech seedlings from contrasting forest litght environments

Leaf-level photosynthetic-light response and plant-level daily carbon gain were estimated for seedlings of moderately shade-tolerant yellow birch (Betula alleghaniensis Britton) and shade-tolerant sugar maple (Acer saccharum Marsh.) and beech (Fagus grandifolia Ehrh.) growing in gaps and under a closed canopy in a sugar maple stand at Duchesnay, Que. All three species had a higher photosynthetic capacity (A(max)) in the gaps than in shade, but yellow birch and beech responded more markedly than sugar maple to the increase in light availability. The high degree of plasticity observed in beech suggests that the prediction that photosynthetic plasticity should decrease with increasing shade tolerance may not hold when comparisons are made among a few late-successional species. Unit-area daily carbon gain (C(A)) was significantly higher in the gaps than in shade for all three species, but no significant difference was observed between light environments for plant-level carbon gain (C(W)). In shade, we found no difference of C(A) and C(W) among species. In gaps, beech had a significantly higher C(A) than sugar maple but similar to that of birch, and birch had a significantly higher C(W) than maple but similar to that of beech. Sugar maple consistently had lower carbon gains than yellow birch and beech but is nevertheless the dominant species at our study site. These results indicate that although plant-level carbon gain is presumably more closely related to growth and survival of a species than leaf-level photosynthesis, it is still many steps removed from the ecological success of a species

Physiological responses of two tropical weeds to shade. I. Growth and biomass allocation

Ipomoea asarifolia (Desr.) Roem. & Schultz (Convolvulaceae) e Stachytarpheta cayennensis (Rich) Vahl. (Verbenaceae), duas plantas invasoras encontradas em pastagens e áreas agrícolas da Amazônia brasileira, foram cultivadas durante 40 dias, em câmaras de crescimento sob alto (800-1000 µmol m-² s-¹, "sol") e baixo (200-350 µmol m-² s-¹, "sombra") regime de luz. Em ambas as espécies a razão de massa e de área foliar por unidade de massa total da planta, e a área foliar por unidade de massa foliar foram maiores na sombra, enquanto a proporção de biomassa alocada para as raízes foi maior nas plantas ao sol. Em S. cayennensis a alocação de biomassa para tecido reprodutivo foi maior nas plantas ao sol, sugerindo uma provável menor habilidade dessa espécie de se manter sob condições de sombreamento. A taxa de crescimento relativo (TCR) em I. asarifolia foi, inicialmente, maior nas plantas ao sol, e após 20 dias passou a decrescer, tornando-se semelhante entre tratamentos nas últimas duas avaliações (aos 30 e 40 dias). Em S. cayennensis, a TCR foi também maior em plantas ao sol, porém esta tendência não foi significativa na primeira e última avaliação (10 e 40 dias). Esses resultados são discutidos com relação às suas importâncias ecológica e de manejo.Ipomoea asarifolia (Desr.) Roem. & Schultz (Convolvulaceae) and Stachytarpheta cayennensis (Rich) Vahl. (Verbenaceae), two weeds found in pastures and crop areas in Brazilian Amazonia, were grown in controlled environment cabinets under high (800-1000 µmol m-² s-¹) and low (200-350 µmol m-² s-¹) light regimes during a 40-day period. For both species leaf dry mass and leaf area per total plant dry mass, and leaf area per leaf dry mass were higher for low-light plants, whereas root mass per total plant dry mass was higher for high-light plants. High-light S. cayennensis allocated significantly more biomass to reproductive tissue than low-light plants, suggesting a probably lower ability of this species to maintain itself under shaded conditions. Relative growth rate (RGR) in I. asarifolia was initially higher for high-light grown plants and after 20 days started decreasing, becoming similar to low-light plants at the last two harvests (at 30 and 40 days). In S. cayennensis, RGR was also higher for high-light plants; however, this trend was not significant at the first and last harvest dates (10 and 40 days). These results are discussed in relation to their ecological and weed management implications.

Functional ecology of advance regeneration in relation to light in boreal forests

This paper reviews aspects of the functional ecology of naturally established tree seedlings in the boreal forests of North America with an emphasis on the relationship between light availability and the growth and survival of shade tolerant conifers up to pole size. Shade tolerant conifer species such as firs and spruces tend to have a lower specific leaf mass, photosynthetic rate at saturation, live crown ratio, STAR (shoot silhouette area to total needle surface area ratio), and root to shoot ratio than the shade intolerant pines. The inability of intolerant species such as the pines and aspen to survive in shade appears to be mainly the result of characteristics at the shoot, crown, and whole-tree levels and not at the leaf level. Although firs and spruces frequently coexist in shaded understories, they do not have identical growth patterns and crown architectures. We propose a simple framework based on the maximum height that different tree species can sustain in shade, which may help managers determine the timing of partial or complete harvests. Consideration of these functional aspects of regeneration is important to the understanding of boreal forest dynamics and can be useful to forest managers seeking to develop or assess novel silvicultural systems

Individual and non‐additive effects of exotic sap‐feeders on root functional and mycorrhizal traits of a shared conifer host

Forest pests drive tree mortality through disruption of functional traits linked to nutrient acquisition, growth and reproduction. The impacts of attack by individual or multiple above‐ground herbivores on root functional traits critical to tree health have received little attention. This is especially true for exotic herbivores, organisms often found in disturbed forests. We excavated whole‐root systems from eastern hemlock (Tsuga canadensis) individuals experimentally infested with hemlock woolly adelgid (HWA: Adelges tsugae) and elongate hemlock scale (EHS: Fiorina externa) individually, or in combination, for periods of 2 and 4 years. Below‐ground root biomass, functional traits and storage nutrients were measured to assess impacts of herbivory. We also quantified ectomycorrhizal fungal (EMF) colonisation of fine roots and used culture‐independent methods to examine EMF diversity. Trees infested with HWA had a greater root mass fraction (root to total biomass ratio), although feeding had no observable effects on root functional traits (e.g. specific root length) or on resource allocation to roots. HWA feeding did significantly reduce EMF colonisation of hemlock fine roots, though surprisingly, EMF diversity and that of other fungal associates were unaffected. In contrast to HWA, EHS (alone or in conjunction with HWA) feeding had no observable effect on below‐ground traits or EMF colonisation alone; however, its presence mediated HWA effects when trees were co‐infested. Simultaneous infestation within the same year yielded significant reductions in EMF colonisation, whereas prior EHS attack weakened HWA effects. Our results collectively suggest that prior EHS attack dampens the impact of HWA on below‐ground functional traits. This highlights how the timing and sequence of herbivore arrival can alter plant‐mediated interactions between herbivores and their effects on above–below‐ground linkages and associated tree health

Growth and morphological response of yellow birch, sugar maple beech seedlings growing under a natural light gradient

Height and lateral growth, biomass distribution, leaf morphology, and crown architecture were studied in yellow birch (Betula alleghaniensis Britton), sugar maple (Acer saccharum Marsh.), and beech (Fagus grandifolia Ehrh.) seedlings growing under 1-50% of above-canopy light in a sugar maple stand, in Quebec. All three species showed increasing growth with increasing light, but growth of yellow birch was higher and more responsive than that of sugar maple and beech. All three species showed typical sun-shade morphological responses, such as decreasing specific leaf area and leaf area ratio, and increasing leaf area index, with increasing light availability. Sugar maple was morphologically more plastic than the other species. It showed variations in biomass allocation to leaves and branches, a decrease in branch length to seedling height ratio, and a marked increase in the ratio of leaf area to stem length. Although our results clearly demonstrate the ability of these three species to modify several of their morphological features in response to variations in light, they do not show a clear relationship between species shade tolerance and morphological response to light variations. We suggest that species-specific developmental patterns may act as important constraints to morphological acclimation to light variation

Role of breastfeeding in disease prevention

\ua9 2024 The Author(s). Microbial Biotechnology published by John Wiley & Sons Ltd.Human milk provides the infant with many bioactive factors, including immunomodulating components, antimicrobials and prebiotics, which modulate the infant microbiome and immune system maturation. As a result, breastfeeding can impact infant health from infancy, through adolescence, and into adulthood. From protecting the infant from infections, to reducing the risk of obesity, type 1 diabetes and childhood leukaemia, many positive health outcomes are observed in infants receiving breastmilk. For the mother, breastfeeding protects against postpartum bleeding and depression, increases weight loss, and long-term lowers the risk of type 2 diabetes, breast and ovarian cancer, and cardiovascular diseases. Beyond infants and mothers, the wider society is also impacted because of avoidable costs relating to morbidity and mortality derived from a lack of human milk exposure. In this review, Medline was used to search for relevant articles to discuss the health benefits of breastfeeding and its societal impact before exploring future recommendations to enhance our understanding of the mechanisms behind breastfeeding\u27s positive effects and promote breastfeeding on a global scale

REGENERATION PATTERNS IN SILVICULTURAL OPENINGS OF WESTERN GREAT LAKES NORTHERN HARDWOOD FORESTS 15-24 YEARS POST-HARVEST

In managed northern hardwood forests, successful forest regeneration can depend on the application of silvicultural methods tailored to stand-specific recruitment limitations. The objective of this research is to develop a deeper understanding of the factors that interfere with tree regeneration at three long-term, well-replicated experimental canopy gap studies in the upper Great Lakes region, USA. Chapter 2 examines regeneration at a hemlock canopy gap study 18 years post-harvest that included deer exclosures and a gradient of gap sizes. Chapter 3 investigates the spatial patterns of low-density regeneration along gradients of gap size and different levels of legacy-tree retention at two canopy gap studies, 15 and 24 years post-harvest. Our findings indicate that deer exclusion in larger gap sizes may promote the recruitment of browse sensitive species, such as yellow birch (Betula alleghaniensis Britton) and eastern hemlock (Tsuga canadensis L.), into the tallest layers of the regeneration response (Chapter 2). Furthermore, spatial patterns of low-density regeneration did not follow resource gradients at the gap level and legacy-tree retention appeared to moderate the extent of low-density regeneration (Chapter 3). Collectively, these studies suggest that reducing herbivory and retaining legacy-trees where appropriate may help secure a timely and species-rich regeneration response